This invention is related to processes for the preparation of chloromethanes such as methylene chloride and chloroform by the thermally initiated vapor phase chlorination of methyl chloride and methylene chloride.
Vapor phase chlorination of methyl chloride and methylene chloride in an adiabatic reactor is generally known The exothermicity of such reactions is well known and can result in serious problems including carbonization of the products and by-product formation as well as explosive hazards. One method of controlling the exothermic nature of the reaction is to limit the chlorine concentration which in turn limits the extent of the reaction. Such a limitation placed on chlorine concentration also limits other reaction parameters such as product mix and the amount of methyl chloride and methylene chloride which may be converted per pass through the reactor. An additional problem associated with vapor phase chlorination is incomplete conversion of the chlorine. The presence of even very small amounts of chlorine in the process downstream of the chlorination reactor can be extremely detrimental to equipment and can produce undesirable impurities in the products.
Various approaches to improving chlorination processes have been proposed. U.S. Pat. No. 2,829,180 teaches the use of a fluidized bed along with an inert diluent, in liquid or vapor form, to control the explosive tendencies of the reaction of chlorine and methane. The primary focus of this process is to produce a product containing a predominating proportion of chloroform. U.S. Pat. No. 2,857,438 teaches the use of liquid coolant in a process for the preparation of perchlorinated products such as carbon tetrachloride and tetrachloroethylene. The primary goal of this process is to produce a product containing high yields of carbon tetrachloride and tetrachloroethylene while minimizing yields of various by-products such as chloroform.
As is clear from a review of these references, the results desired and the process steps capable of obtaining desired results vary from process to process. Thus, what is needed is an improved method for the adiabatic vapor phase chlorination of methyl chloride and methylene chloride that eases the limits placed on chlorine concentration: gives flexibility in product mix; and improves reactor volumetric efficiency.